The monkeypox virus, which has now been diagnosed in hundreds of people in 26 countries, may have been circulating quietly for years before its sudden emergence around the world, some scientists say.
Infectious disease experts and scientists in genetics labs are urgently looking for clues as to why a virus that has been found in West Africa for half a century and usually does not spread easily from person to person to Another has made such a dramatic and disturbing appearance in the past month. “‘There may have been undetected transmission for some time,’ Dr. Rosamund Lewis, the World Health Organization’s technical lead for monkeypox, said during a briefing on Wednesday. “What we don’t know is how long it may have lasted. I don’t know if it’s weeks, months or maybe a few years.
At the University of Leuven in Belgium, virology professor Marc Van Ranst told NBC News that sequencing from his lab revealed genetic mutations in the virus that were “limited” and “none of them is irrefutable proof.
“Everyone is interested in more complete genomes to get a sense of a pretty big question: How long have these viruses been circulating under the radar?” said Van Ranst. “I don’t think anyone believes it jumped out of Africa a few weeks ago.”
Scientists at the University of Edinburgh recently sequenced samples from the outbreak and published their results on May 30. The samples they studied came from a version of monkeypox that was identified in Singapore, Israel, Nigeria and the UK between 2017 and 2019.
Although investigators have identified an “unexpected number” of changes in the genetic code of the virus since then, some experts do not believe these changes necessarily explain the scale of the current outbreak.
In Africa, most human cases of monkeypox have historically occurred through exposure to infected animals such as rodents and not through person-to-person transmission.
“What probably happened was that an infectious disease endemic to Africa found its way into a social and sexual network and then was greatly aided by major amplifying events like raves in Belgium for spread around the world,” said lead researcher Dr. Amesh A. Adalja. at the Johns Hopkins Center for Health Security, said.
“And then,” Adalja added, “because it’s transmitted through close contact during sexual encounters, many lesions are mistaken for other sexually transmitted infections, which can delay diagnosis.”
Increased vigilance by public health authorities, healthcare providers and individuals around the world has dramatically improved detection in recent weeks.
“Every time you start looking for a disease that’s new to a population, you find many, many more cases,” said Dr David Heymann, a teacher at The London School of Hygiene and Tropical Medicine, which previously led the WHO’s program on emerging and other communicable diseases, told NBC News.
Heymann supported the theory that the disease may have been present in some populations for several years outside the 11 countries in central and west Africa where the virus has become endemic. Cases may be circulating stealthily among people outside the global gay community, he suggested.
“The concern is with a single population rather than looking more broadly,” he said.
Very mild symptoms of monkeypox
The infection, which can cause painful lesions all over the body that leave lasting scars, usually runs its course in an individual in about three weeks. Most of the cases identified in Europe and the United States have been mild – some so atypically subtle that they have been mistaken for other sexually transmitted infections – and have occurred in gay men, bisexuals and other men with sex with men. Experts point out, however, that it is the close physical contact of sexual activity that is the key factor in transmission.
Contrary to what is typically seen in monkeypox cases in Africa, some of the recent infections have resulted in “very, very mild” symptoms, possibly involving a single lesion, said hospital infectious disease specialist Dr Sebastien Poulin. St-Jerome of Montreal. who diagnostic one of the first outbreak cases in Canada, NBC News told NBC News. “Doctors need to be aware of this.”
Additionally, monkeypox disease usually begins with a fever, but some of the recent cases in the United States did not report fever or other early signs before the lesions appeared, according to the Centers for Disease Control and Prevention.
“For this reason, cases may be confused with more common infections such as varicella zoster or sexually transmitted infections,” such as genital herpes or syphilis, a CDC study published Friday reported.
Sixty-six people died from the infection in African countries in 2022, according to the World Health Organization. Nigeria has been battling its own outbreak of monkeypox since 2017 – an outbreak that may have served as an incubator for global spread.
There have been no deaths in the current outbreak in Europe or the United States, although in the United States at least one person has been hospitalized for treatment of severe pain caused by lesions in the anal region, the Capt. Jennifer McQuiston, deputy director of the CDC’s High Consequence Pathogens and Pathology Division, said during a Friday briefing.
Van Ranst said the next few days of the outbreak will be key to controlling the disease. As of June 1, there were 643 confirmed cases, according to the WHO. If by next week the cumulative number of cases follows an exponential curve and reaches maybe 4,000, “then it’s not under control,” he said.
If the figure only increases to around 1,000, then the epidemic is likely only growing in a linear fashion, which bodes well for global control of the virus, Van Ranst said.